Such a filter arrangement is known, for example, from EP 2 133 130 A. The transmission oil filter known from EP 2 133 130 is intended to be suitable as a suction filter. This filter is constructed as a filter according to the so-called “partial flow” principle and comprises a first filtration layer, which is in the form of an open coarse filter, and also a second filtration layer, which is in the form of a tight fine filter. The filtration layers are arranged spaced apart, with the interposition of a support grid. The transmission oil filter is constructed and designed in such a way that the oil firstly flows through the tighter filtration layer and then enters into the intermediate chambers formed between the filtration layers, and finally leaves the filtration medium via the first, less tight filtration layer. In order to ensure that oil can flow through with relatively low pressure losses even when it is cold, flow openings or flow bypasses are arranged in the tighter filtration layer. The entire arrangement, comprising two filtration layers and the frame element arranged therebetween, is usually arranged in a filter housing in such a way that the entire oil flow passes through the filter arrangement.
The engine oil circuit of motor vehicles, in particular transmission oil circuits, contains significant proportions of ferritic particles, which are normally kept out of the oil flow by means of one or more magnets. The magnets are arranged in a filter housing surrounding the filter arrangement, in such a way that the greatest possible proportion of the volumetric flow of oil flows around them.
This known magnet filter arrangement is tainted with the disadvantage that the magnets have to have a relatively high magnetic field strength, so that they can hold magnetizable particles even in the case of strong flow dynamics. This is aggravated by the fact that, in the case of cold transmission oil and a corresponding viscosity of the oil, the magnets are exposed to high shearing forces in the region of the circulating flow, and therefore this can lead to the magnets being cleaned off, with the result that the ferritic particles pass back into the oil circuit.
Magnets with an appropriately high holding force/magnetic field strength are expensive and take up a relatively large amount of space in the oil filter housing.